1. Field of the Invention
This invention is in the field of aircraft, and particularly relates to a landing gear system adapted to absorb and distribute the energy of a non-level landing and to restore the aircraft to its proper attitude with respect to the ground following such a landing.
2. The Prior Art
In U.S. Pat. No. 2,368,855 issued Feb. 6, 1945 to Levy, there is disclosed a two-stage hydraulic landing gear system. Each of the landing gears includes a relatively soft upper dashpot and a relatively stiff lower dashpot. As one of the wheels contacts the ground, hydraulic fluid is expressed from the upper dashpot into an accumulator and energy is absorbed in the process. The upper dashpots of each of the landing gears communicate so that if one of the wheels strikes the ground before the others do, the other landing gears will be extended by the transfer of fluid. Because the upper dashpots in each of the landing gears are relatively soft, as the full weight of the aircraft is applied, the upper dashpots reach the end of their stroke and are locked in this fully-compressed condition. Thereafter, during taxiing of the aircraft, only the relatively stiff lower dashpots are effective.
This system would appear to have problems in the event of a landing in which the aircraft rocks from one side to the other, as commonly occurs with helicopters. If the landing gear on one side of the aircraft were to become locked and the landing then aborted, the second landing attempt would be complicated by the unequal lengths of the landing gears.
In U.S. Pat. No. 3,327,974 issued June 27, 1967, Nicholl discloses a landing gear apparatus in which a reversable actuator transfers liquid from the piston of one landing gear to the piston of another landing gear. The load on each landing gear is sensed and the difference in the loads is calculated. The more highly-loaded gear is contracted to change the trim of the aircraft to reduce the difference in loads.
This system is relatively complex since it requires both sensing as well as the controlled application of power to transfer the liquid.
In U.S. Pat. No. 3,042,345 issued July 3, 1962 to Holland, Jr., there is disclosed in FIGS. 18-20 an interconnected hydraulic landing gear apparatus. Cylinders in each landing gear are connected so that if the aircraft hits on one of the landing gears first, compressing it, the other landing gears are extended. This would appear to cause the aircraft to tilt even more severely, and is not necessarily desirable. Further, there is no provision for restoring the aircraft to a proper attitude with respect to the ground. A similar system is shown in U.S. Pat. No. 2,519,522 issued Aug. 22, 1950 to Wells.
In U.S. Pat. No. 4,004,762 issued Jan. 25, 1977, Jenkins discloses an electrically operated system for maintaining the mean height of the aircraft above the ground.
Thus, although systems are known in the art to perform related functions, no system is known to perform the functions of the present invention or to possess its advantageously simple structure.